With rapid development in 3D conformal radiation therapy and stereotactic radiotherapy, which tends to treat small and highly tailored clinical targets with very high doses, increasingly stringent setup accuracy become more important. Currently, many researches in early tumor detection use imaging techniques such as CT, MRI, and SPECT, treatment plan optimization using inverse planning, and beam management using IMRT and SRT. There are lack of development in patient refixation technique. The primary objective of the SBIR effort proposed herein is to develop a novel patient refixation technique feasible for daily treatment of fractionated radiotherapy. The technique can achieve a high accuracy and precision within 1-mm by using a novel high-speed three-dimensional (3D) video camera. The precise 3D-surface images of patient can be captured following the patient positioned on the treatment couch. The surface images are compared with the reference 3D image that is created from the previous CT scans or 3D-video image with the patient in the planned treatment position. The 3D surface fitting and frame subtraction techniques will generate quantitative parameters regarding patient?s positioning error in all six degree-of-freedom, facilitating the re-position adjustment. Because the video image is acquired instantly, this frame-less patient refixation system also provides a solution for the real-time detection and correction of patient motion relative to the treatment machine in a single fraction. In the proposed Phase 1 effort, we will (1) Design an accurate patient refixation system using a 3D video camera; (2) Build prototype hardware of the 3D video camera and assess the clinical feasibility; (3) Develop the proposed 3D image subtraction and comparison algorithms to unfold patient positioning error; (4) Improve the software tools to interactively visualize and rapidly quantify 3D positioning errors; and (5) Perform patient reposition experiments. PROPOSED COMMERCIAL APPLICATION: The proposed 3D imaging technology adds one more dimension (literally and figuratively) to fractional radiation treatment repositioning applications, and will lead to a new generation of commercial products of patient repositioning systems for radiotherapy. With hundreds of radiation treatment machines in USA and many more in Europe, the market for a clinically acceptable 3D-camera-based refixation system is significant. If it succeeds, it will have a significant impact on biomedical research and will revolutionize many current practices in rafixation during cancer treatment. It would find utility in reconstructive surgery due to cancer, body deformities, orthotics, rehabilitation, resident training and education.